Fun

Gentle Arms of Eden.

Evolution

Public acceptance of evolution

(Miller, Scott, & Okamoto, 2006)

Types of evidence

  • Fossil
    • Fossil dating
  • Geological
    • Where fossils are found relative to one another
    • How long it takes to form layers
  • Genetic
    • Rates of mutation
  • Anatomical

Nothing in Biology Makes Sense Except in the Light of Evolution

“Seen in the light of evolution, biology is, perhaps, intellectually the most satisfying and inspiring science. Without that light, it becomes a pile of sundry facts some of them interesting or curious, but making no meaningful picture as a whole.”

(Dobzhansky, 1973)

Why Gilmore thinks the theory so controversial (in the U.S.)?

  • Contradicts verbatim/non-metaphorical reading of some religious texts
  • Makes humans seem less special
  • Time scales involved beyond human experience
  • Scientific method vs. other ways of knowing
  • Found in nature ≠ good for human society
  • Few negative consequences of ‘disbelief’
  • U.S. culture individualistic, skeptical, anti-elitist/anti-intellectual
  • Lower levels of religious belief among U.S. scientists
  • Politics
  • A minority of citizens support teaching evolution-only
  • Majority of classroom teachers aren’t strong advocates

Evolution and development

Ontogenesis and phylogenesis

  • Ontogenesis
    • Development within lifetimes, history of individuals
  • Phylogenesis
    • Change across lifestimes, history of species

Nervous system architectures

An animal with a nerve “net”

How nervous systems differ

  • Body symmetry
    • radial
    • bilateral
  • Segmentation
  • Cephalization (concentration of sensory & neural structures in anterior portion of body)
  • Encasement in bone (vertebrates)
  • Centralized vs. distributed function

Cephalopods have “intelligent arms”

What nervous systems must do: Biological computation

  • Ingestion
  • Defense
  • Reproduction

Information processing universals

  • Sense/detect
    • Sensors
  • Analyze, evaluate, decide
  • Act
    • Effectors
    • e.g., approach/avoid, manipulate, ingest, signal

Sensors

  • Specialize by information source/type
  • Specialize by target location
    • Interoceptive
    • Exteroceptive

Analysis, evaluation, decision

  • Current state
    • World
    • Organism
  • Current goals
  • Past state(s)

Effectors

  • Move body
  • Send signals
  • Change physiological state

From nerve net to nerve ring, nerve cord and brain

(Arendt, Tosches, & Marlow, 2016)

  • Neurons and nervous systems 520-570 M years old
  • Similarities at molecular level in how diverse nervous systems develop

Vertebrate CNS organization

(Northcutt, 2002)

(Northcutt, 2002)

(Hofman, 2014)

Structural measure Non-human comparison Human
Cortical gray matter %/tot brain vol insectivores 25% 50%
Cortical gray + white mice 40% 80%
Cerebellar mass primates, mammals 10-15% 10-15%

(Rakic, 2009)

(Hofman, 2014)

Take homes

  • Brain sizes scale with body size
  • Brain sizes scale with animal class (more or less)

Old story

  • Within mammals, human brains bigger than expected
    • Higher encephalization quotient
  • Humans have larger cerebral cortical gray + white matter than comparable mammals

vs. New story

  • Does brain size/mass matter (that much)?
  • “Size matters” (brain mass) presumes similarity among brains at micro-level
  • Big (large mass) brains arise in multiple animal lineages

  • # of cortical neurons more important difference than brain mass
  • The primate advantage -> more cortical neurons, but not larger neurons
  • Human brain just scaled up (non-ape) primate brain

# of cortical (or in birds, pallidum) neurons predicts “cognition”?

(Herculano-Houzel, 2017)

The Human Advantage (Herculano-Houzel, 2016)

  • More neurons in cerebral cortex than other animals, but not disproportionately so
  • Less time spent foraging
    • Higher quality/more energetically dense food
    • Higher food availability
    • Cultural factors (agriculture + cooking)
    • See also (Wrangham, 2009)

A further human advantage

Human brain development

Prenatal brain development

Insemination

  • 3-4 days before or up to 1-2 days after…
    • Ovulation

Fertilization

  • Within ~ 24 hrs of ovulation

Implantation

  • ~ 6 days after fertilization

Early embryogenesis

Formation of neural tube (neurulation)

  • Embryonic layers: ectoderm, mesoderm, endoderm
  • ~18-26 days
  • Failures of neural tube closure
    • Spina bifida
    • Anencephaly
  • Neural tube becomes
    • Ventricles
    • Central canal of spinal cord

Neurogenesis and gliogenesis

  • Neuroepithelium cell layer lines neural tube
  • Neural stem cells - Undergo symmetric & asymmetric cell division - Generate glia, neurons, and basal progenitor cells

(Götz & Huttner, 2005)

Zika and microcephaly

Radial glia

Cell migration

Radial unit hypothesis

(Rakic, 2009)

Migration

Glial migration

(Baumann & Pham-Dinh, 2001)

Axon growth cone

Axons follow

  • Chemoattractants
    • e.g., Nerve Growth Factor (NGF)
  • Chemorepellents
  • Receptors in growth cone detect chemical gradients

Differentiation

  • Neuron vs. glial cell
  • Cell type
  • NTs released
  • Where to connect

Differential gene expression in PFC vs. other

[johnson2009functional]

Infancy & Early Childhood

Synaptogenesis

Proliferation, pruning

  • Early proliferation
  • Later pruning
  • Rates, peaks differ by area

Apoptosis

  • Programmed cell death
  • 20-80%, varies by area
  • Spinal cord >> cortex
  • Quantity of nerve growth factors (NGF) influences

(Rakic, 2009)

Synaptic rearrangement

  • Progressive phase: growth rate >> loss rate
  • Regressive phase: growth rate << loss rate

Myelination

(Baumann & Pham-Dinh, 2001)

  • Neonatal brain largely unmyelinated
  • Gradual myelination, peaks in mid-20s
  • Non-uniform pattern
    • Spinal cord before brain
    • Sensory before motor

Structural development

(Knickmeyer et al., 2008)

Postnatal patterns of synaptogenesis

Myelination across human development

(Hagmann et al., 2010)

Networks in the brain

(Irimia & Van Horn, 2014)

Functional connectivity

Age-related profiles in connectivity among “control networks.”

Age-related profiles in connectivity among “non-control networks.”

The “development” of developmental connectomics

(Cao, Huang, & He, 2017)

Myelination changes “network” properties

(Hagmann et al., 2010)

Synaptic rearrangment, myelination change cortical thickness

(Gogtay et al., 2004)

Changes in brain energetics

(Kuzawa et al., 2014)

Glucose utilization across age.

Gene expression across development

(Kang et al., 2011)

Summary of developmental milestones

Prenatal

  • Neuro- and gliogenesis
  • Migration
  • Synaptogenesis begins
  • Differentiation
  • Apoptosis
  • Myelination begins
  • Infant gene expression ≠ Adult

Postnatal

  • Synaptogenesis
  • Cortical expansion, activity-dependent change
  • Then cubic, quadratic, or linear declines in cortical thickness
  • Myelination
  • Connectivity changes (esp within networks)
  • Prolonged period of postnatal/pre-reproductive development (Konner, 2011)

How brain development clarifies anatomical structure

3-4 weeks

~4 weeks

Beyond 6+ weeks

Organization of the brain

Major division Ventricular Landmark Embryonic Division Structure
Forebrain Lateral Telencephalon Cerebral cortex
Basal ganglia
Hippocampus, amygdala
Third Diencephalon Thalamus
Hypothalamus
Midbrain Cerebral Aqueduct Mesencephalon Tectum, tegmentum
Hindbrain 4th Metencephalon Cerebellum, pons
– Mylencephalon Medulla oblongata

From structural development to functional development

(Johnson, 2001)

References

Arendt, D., Tosches, M. A., & Marlow, H. (2016). From nerve net to nerve ring, nerve cord and brain — evolution of the nervous system. Nature Reviews Neuroscience, 17(1), 61–72. https://doi.org/10.1038/nrn.2015.15

Baumann, N., & Pham-Dinh, D. (2001). Biology of oligodendrocyte and myelin in the mammalian central nervous system. Physiological Reviews, 81(2), 871–927. https://doi.org/10.1152/physrev.2001.81.2.871

Cao, M., Huang, H., & He, Y. (2017). Developmental connectomics from infancy through early childhood. Trends in Neuroscience, 40(8), 494–506. https://doi.org/10.1016/j.tins.2017.06.003

Chi, J. G., Dooling, E. C., & Gilles, F. H. (1977). Gyral development of the human brain. Ann. Neurol., 1(1), 86–93. https://doi.org/10.1002/ana.410010109

Dobzhansky, T. (1973). Nothing in biology makes sense except in the light of evolution. The American Biology Teacher, 35(3), pp. 125–129. Retrieved from http://www.jstor.org/stable/4444260

Gogtay, N., Giedd, J. N., Lusk, L., Hayashi, K. M., Greenstein, D., Vaituzis, A. C., … Thompson, P. M. (2004). Dynamic mapping of human cortical development during childhood through early adulthood. Proc. Natl. Acad. Sci. U. S. A., 101(21), 8174–8179. https://doi.org/10.1073/pnas.0402680101

Götz, M., & Huttner, W. B. (2005). The cell biology of neurogenesis. Nat. Rev. Mol. Cell Biol., 6(10), 777–788. https://doi.org/10.1038/nrm1739

Hagmann, P., Sporns, O., Madan, N., Cammoun, L., Pienaar, R., Wedeen, V. J., … Grant, P. E. (2010). White matter maturation reshapes structural connectivity in the late developing human brain. Proceedings of the National Academy of Sciences, 107(44), 19067–19072. https://doi.org/10.1073/pnas.1009073107

Herculano-Houzel, S. (2016). The human advantage: A new understanding of how our brain became remarkable. MIT Press. Retrieved from https://market.android.com/details?id=book-DMqpCwAAQBAJ

Herculano-Houzel, S. (2017). Numbers of neurons as biological correlates of cognitive capability. Current Opinion in Behavioral Sciences, 16(Supplement C), 1–7. https://doi.org/10.1016/j.cobeha.2017.02.004

Hofman, M. A. (2014). Evolution of the human brain: When bigger is better. Frontiers in Neuroanatomy, 8. https://doi.org/10.3389/fnana.2014.00015

Irimia, A., & Van Horn, J. (2014). Systematic network lesioning reveals the core white matter scaffold of the human brain. Frontiers in Human Neuroscience, 8, 51. https://doi.org/10.3389/fnhum.2014.00051

Johnson, M. H. (2001). Functional brain development in humans. Nat. Rev. Neurosci., 2(7), 475–483. https://doi.org/10.1038/35081509

Kang, H. J., Kawasawa, Y. I., Cheng, F., Zhu, Y., Xu, X., Li, M., … Šestan, N. (2011). Spatio-temporal transcriptome of the human brain. Nature, 478(7370), 483–489. https://doi.org/10.1038/nature10523

Knickmeyer, R. C., Gouttard, S., Kang, C., Evans, D., Wilber, K., Smith, J. K., … Gilmore, J. H. (2008). A structural MRI study of human brain development from birth to 2 years. J. Neurosci., 28(47), 12176–12182. https://doi.org/10.1523/JNEUROSCI.3479-08.2008

Konner, M. (2011). The Evolution of Childhood. Belknap Press of Harvard University Press. Retrieved from http://www.hup.harvard.edu/catalog.php?isbn=9780674062016

Kuzawa, C. W., Chugani, H. T., Grossman, L. I., Lipovich, L., Muzik, O., Hof, P. R., … Lange, N. (2014). Metabolic costs and evolutionary implications of human brain development. Proc. Natl. Acad. Sci. U. S. A., 111(36), 13010–13015. https://doi.org/10.1073/pnas.1323099111

Miller, J. D., Scott, E. C., & Okamoto, S. (2006). Public acceptance of evolution. SCIENCE-NEW YORK THEN WASHINGTON-, 313(5788), 765. https://doi.org/10.1126/science.1126746

Northcutt, R. G. (2002). Understanding vertebrate brain evolution. Integr. Comp. Biol., 42(4), 743–756. https://doi.org/10.1093/icb/42.4.743

Petrican, R., Taylor, M. J., & Grady, C. L. (2017). Trajectories of brain system maturation from childhood to older adulthood: Implications for lifespan cognitive functioning. Neuroimage. https://doi.org/10.1016/j.neuroimage.2017.09.025

Rakic, P. (2009). Evolution of the neocortex: A perspective from developmental biology. Nature Reviews Neuroscience, 10(10), 724–735.

Shaw, P., Kabani, N. J., Lerch, J. P., Eckstrand, K., Lenroot, R., Gogtay, N., … Others. (2008). Neurodevelopmental trajectories of the human cerebral cortex. Journal of Neuroscience, 28(14), 3586–3594. https://doi.org/10.1523/JNEUROSCI.5309-07.2008

Wrangham, R. (2009). Catching fire: How cooking made us human. Basic Books. Retrieved from https://market.android.com/details?id=book-ebEOupKz-rMC